^HE LUNGS AND RESPIRATION. 207 



tube-s. An inflammation of the mucous membrane of the 

 stomach is called a "catarrh" of the stomach, while even an 

 inflammation of the eye due to exposure is spoken of as an 

 ophthalmic catarrh. 



As long as the inflammation is confined to the larger air 

 passages no especial danger ensues. But this inflammation 

 may become extended into the alveoli of the lung. This 

 condition is a much more serious one, and is called pneu- 

 monia. Colds, catarrh and pneumonia are not, however, 

 mere congestions. If they were, the effects of the conges- 

 tion ought to disappear when the proper vascular supply is 

 re-established. These diseases owe their dire results to the 

 infection of germs. The bacterium of pneumonia has been 

 recently, actually, quite satisfactorily isolated. Arctic ex- 

 plorers report their perfect immunity from colds in regions 

 which are free from bacteria. We must look upon the con- 

 gestion of the air passages or lungs more as a favorable cir- 

 cumstance for bacterial infection, which infection once hav- 

 ing secured a foothold, produces the real disease. That the 

 resistance of the respiratory organs to germs is materially 

 weakened in congestions is attested by the relative ease 

 with which consumption is induced in weak persons, as a 

 consequence of a " cold." 



The pleura, also, may. become the seat of inflammation, 

 giving rise to a disease called pleurisy. 



The smaller bronchial tubes near to where they open 

 into the alveoli, possess in their walls some plain muscular 

 fibres. Ordinarily these are relaxed and so free access of 

 air is permitted to the alveoli. But under certain conditions 

 these muscles go into a tonic contracted state, thus materi- 

 ally reducing the quantity of air which is able to get into 

 the alveolus and so making it difficult for the person in 

 question to get a sufficient amount of air. This condition 

 is called asthma. 



Finally, the most serious pathological condition of the 

 lung is consumption. This, as has been pointed out, is a 

 disease which is due to the ravages of bacteria living in that 



